Abstract
An s-domain analysis of the full dynamics of the pole-zero pair (frequency doublet) associated with the broadly used CMOS active-cascode gain-enhancement technique is presented. Quantitative results show that three scenarios can arise for the settling behavior of a closed-loop active-cascode operational amplifier depending on the relative locations of the unity-gain frequencies of the auxiliary and the main amplifiers. The analysis also reveals that, although theoretically possible, it is practically difficult to achieve an exact pole-zero cancellation. The analytical results presented here provide theoretical guidelines to the design of CMOS operational amplifiers using this technique.
Highlights
Invented in 1979 [1] and subsequently refined in 1990 [2,3,4], the CMOS active-cascode gain-enhancement technique1 finds wide applications in analog integrated circuits, such as Nyquist-rate and oversampling data converters, sample-and-hold amplifiers, switched-capacitor filters, band-gap reference circuits, and voltage regulators
In an attempt to achieve a high unity-gain frequency and a high dc gain simultaneously, the active cascode introduces a pole-zero pair near the unity-gain frequency of the auxiliary amplifier, which potentially leads to slow-settling behavior of such op amps [2]
This paper examines the doublet behavior of CMOS active cascodes
Summary
Invented in 1979 [1] and subsequently refined in 1990 [2,3,4], the CMOS active-cascode gain-enhancement technique finds wide applications in analog integrated circuits, such as Nyquist-rate and oversampling data converters, sample-and-hold amplifiers, switched-capacitor filters, band-gap reference circuits, and voltage regulators. By boosting the low-frequency transconductance of the cascode device, the technique increases the output resistance of a CMOS cascode operational amplifier (op amp), and the voltage gain without degrading its high-frequency performance. As a result, it is ideally suitable for on-chip applications, where a large gainbandwidth product is desirable while driving capacitive loads.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
